Vascular-tubular organization of the human kidney. We have been able to secure a number of normal and pathological kidneys which have not been suitable for renal transplant. These were perfused with glutaraldehyde and will be injected in the same manner as the dog kidneys. Renin-Angiotensin-Aldosterone system in congestive failure. Haber and Poulsen have recently described a simplified radioimmunoassay for plasma aldosterone which will enable us to follow the hourly time course of aldosterone during pulmonary artery constriction in the conscious dog. Electronprobe microanalysis: Our specific aim is to apply this new and powerful method to studies of sodium distribution and sodium handling in regions of the kidney inaccessible to micropuncture. These regions include not only tubular structures deep in the cortex, but also the internal regions of single cells in the proximal tubule and juxtaglomerular apparatus. Specifically, we propose to examine the cells of the juxtaglomerular apparatus and determine how their sodium content varies among animals in different physiologic states, including salt loading, hormone treatment, and experimental heart failure. We wish to compare the sodium content of epithelial cells of superficial and inner cortical proximal tubules. By applying the liquid droplet methods of Dr. Lechene, we intend to measure the composition of tubular fluid in deep parts of the cortex.